Method for operating cupola furnaces



Patented May 16, 19.39

METHOD FOR OPERATING CUPOLA FURNACES Lauer, Gelsenkirchen, Germany, assignor to Dentsclie Eisenwerke Aktiengesellschaft, Mulhetigi-on-the-Ruhr, Germany, a body co pora No Drawing. Application June 16, 1938, Serial No.- 214,045. In Germany June 19, 1937 10 Claims. (01. 75-43) It is known in foundry practice, when melting cast iron in a cupola furnace, to add to the iron charge a more or less great percentage of steel scrap, wrought iron waste or other iron poor in Whereas hitherto in normal iron charges a normal minimum quantity of coke was necessary for every furnace in practical service, which quantity could certainly not be reduced when' steel was added to the iron charge, it is absolutely contrary to all hitherto known proposals and to all former practice to work according to the present method, independently of the kind of iron charge, in all instances in continuous servit is possible, especially in the'case of bad qualities of coke with high sulphur content, to considerably reduce the quantity. of charge coke without. unfavourabiy influencing the running temperature'of the outflowing iron. In the prescarbon, and as far as possible in lumps of relaice with small quantities of charge coke hitherto tively coarse and large cross-section adapted to not considered practically possible and yet at the the diameter of the furnace, and for melting of same time to be able to continually melt a sufilsuch charges to use only the quantities of coke ciently hot iron, as, in spite of the reduced quanusual for the remelting of pig iron or pig iron tity of charge coke extremely favourable furnace m and broken cast iron. The steel addition to the conditions with sufliciently high temperatures charge has for its object to reduce the carbon are produced owing to the burning of the added content of the molten iron and also effects an' inferior steel wool or the like. increase of the melting temperature. To obtain the best possible utilization of the Steel and wrought iron wastes have also been combustion heat of the steel wool or the like,

L used in the form of chips or sheet waste as steel the steel wool serving as heat generating means addition to the cupola iron charge. These inis preferably charged with the coke and mixed ferior small piece wastes have either been introtherewith. Consequently, this steel wool or the duced into the melting zone of the furnace in like is not taken into consideration in calculatcompressed state with the aid of an eccentric ing and compiling the iron charge especially as '2 press or they have been charged with the iron it has scarcely any or no direct influence on the charge in as compressed a state as possible in composition of the molten iron. suitable sheet metal containers, or briquetted into Owing to its small cross sectional and large tightly compressed state with or without binding superficial area the steel wool or the like very agent, when in most instances an increase of quickly assumes an extremely high temperature the quantity of charge coke was considered necin the furnace and burns in the melting zone essary. In all theseremelting processes, howdeveloping great speciflcheat, so that it is absoever, a considerable loss of iron cannot be lutely possible, with relatively small additions of avoided. steel wool, to replace a considerable portion of Concerning the consumption in charge coke the normal usual quantity of charge coke.

of cupola furnaces, i. e., the quantity of coke to It is easily possible with the aid of this novel be used in the furnace for each iron charge, it process to replace to and even up to was heretofore generally considered necessary of the normal usual charge coke by a considerthat at least 8 to 10% charge coke be used for ably less great quantity by weight of steel wool obtaining perfect, sufliciently not running cast or the like, namely by an addition amounting to 35 iron in. continuous service. as much as 30% of the weight of the normal 35 The inventor of the present method has discharge coke.

covered that, on the one hand, the considerable Although--as in all remelting processes of amount of heat developed by the unavoidable small lump steel wastes-an iron loss occurs in loss of steel waste and the like can be utilized the present method by the almost complete 40 economically in a surprising manner in the heat burning of the steel wool or the like, the novel 40 balance of the cupola furnace and, on the other method, owing to the'relatively light weight and hand, that e furnace can actually be operated low value of the necessary quantities of steel in continuous service with a smaller quantity of wool or the like, ensures a very excellent econcharge coke than usual, in that, under otherwise omy, as not only as much as half or even more of 13 similar conditions, the portion of coke lacking the normal charge coke is saved but as forthis 4 from the usual quantity of charge coke can be large quantity of coke saved a much smaller replaced by steel wool or similar iron poor in quantity by weight of steel wool or the like can carbon, of large surface and smallcross section be substituted which is in any case difllcult to introduced into the furnace as a heat generating briquette p b y u e otherwlsemeans in loose' state. Another advantage of the new method is, that 50 cut invention, which allows an, increased charge passage owing to the quantitatively and specially reduced quantities of fuel, it has been unexpectedly found, that the running temperature, as compared with the running temperature of cast iron melted with the normal quantity of coke, is not only as high but may be even higher with correctly measured wooladdition corresponding to the reduction of charge coke and with blast conditions adapted to this wool addition.

Owing to the considerably reduced quantity of charge coke there is in the cupola furnace generally sufllcient wind, that is oxygen, for the whole burning procedure in the method according to the invention. However, the expert will have no difllculty in regulating, according to the quantity of steel wool or the like and according to the type of furnace, these conditions corresponding to the actual reduced quantity of charge coke and to the actual quantity of steel wool ascregards the quantity of air and blast pressure in a manneriproducing best conditions of combustion and highest running temperatures of the outfiowing iron. Thus, in many instances it may be necessary to increase the quantity of air or blast pressure relatively to the blast conditions usual when melting with normal usual charge coke, and in other instances a reduction may possibly be advisable depending upon the quantity of the steel wool addition.

An advantage worth mentioning of the present method from a metallurgical point of view is that, owing to the reduced quantity of charge coke, considerably less sulphur enters the furnace than heretofore so that the cast iron produced turns out extremely poor in sulphur :without any additional measure being employed.

It is also possible to work with considerably smaller additions of lime than hitherto, with the result that less heat is required for melting the reduced quantity of lime, this resulting either in a saving in fuel or in' a better utilization of the available heat for increasing the temperature of the molten iron.

The novel method is suitable for melting cast iron from all iron charges; thus, the charge may consists, for example, nearly of pig iron and of broken cast iron, but steel or similar iron poor in carbon may also be used in any quantity as a charge constituent. Owing to the small quantity of charge coke and owing to the high melting zone temperature a high duty cast iron oi high temperature will be. obtained especially in the latter instance.

Exhaustive tests carried out with the method according to the invention have given the fol;

lowing results: A cupola furnace, in which pig.

iron and broken cast iron were employed as charge, each iron charge of 900 kiiogrammes, hitherto required a quantity 'of charge coke amounting to 90 kilogrammes per iron charge.

According to the novel method the same furnace was operated with the same iron charge of 900 kilogrammes in such a manner that for each iron charges only kilogrammes of charge coke were employed in which 15 kilogrammes of steel wool were distributed. In this manner 10 charges were melted successively and'the running temperature remained practically unchanged during the melting down of the charges;

it amounted to about 1360 to 1380" C.- On the other hand the iron melted according to the novel method was considerably poorer in sulphur than the iron melted in the usual manner with the usual quantity of charge coke, and fu thermore the costs of the melting were considerably lower, as 45 kilogrammes of coke were replaced by only 15 kilogrammes of steel wool, with the result that a saving of 0.75 mk. to 1 mk. per ton of molten cast iron was obtained.

Instead of steel wool, otherloose large-surface, small cross sectional steel wastes, such as sheet wastes, sheet iron boxes or the like may be used as heat carriers.

I claim:

1..A method for operating cupola furnaces, which method consists in operating the furnace with a smaller quantity of charge coke than usual and substituting for the lacking portion of the usual quantity of charge coke easily oxidizable metal pieces of small cross-section and large surface chargedinto the furnace in loose condition and acting as heat generating means.

2. A method for operating cupola furnaces, which method consists in operating the furnace with a smaller quantity of .charge coke than usual and substituting for the lacking portion of the usual quantity of charge coke easily oxidizable iron pieces poor in carbon of small crosssection and large surface, charged into the furnace in loose condition and acting as heat generating means.

3. A method for operating cupola furnaces, which method consists in operating the furnace with a smaller quantity of charge coke than usual and substituting for the lacking portion of the usual quantity of the charge coke easily oxidizable steel wool of small cross-section and large surface, charged into the furnace in loose condition and acting as heat generating means. M

a. A method as' specified in claim 1, in which the easily oxidizable metal serving as heat generatlng means is introduced into the furnace together with the coke.

5. A. method for operating cupola furnaces, which method consists in operating the furnace with 9. quantity oi charge'colse from d0% to less than the usual quantity of charge coke, the lacking quantity of charge coke being replaced by a steel wool addition amounting to from 15% to 30% of the usual Weight of the charge coke.

6. A method as specified in claim 1, in which aluminium waste forms at least part of the easily oxidizable metal.

7. A method as specified in claim 1, in which the furnace is charged with pig iron and broken cast iron to produce cast iron.

8. A method as specified in claim 1, in which the cupola iron charges contain steel for providing high-duty cast iron 01 high temperature.

9. A'method as specified in claim 1, in which the cupolairon charges contain iron poor in carbon for providing high-duty cast iron of high temperature.

10. A method, as claimed in claim 1, in which .the material serving as heat generating means is introduced into the furnace together and mixed with the coke.

KARL LAUER. 

